Slitherine

When the Russians declare you have one turn to act before they show up. My new favourite way of facing them is to take Warzaw on that very turn. All it takes is the two inf units starting in the east and one garrison or other ground unit. Make sure all three can reach Warzaw. If you want to you could also strike with your fighter but I think this might put it in danger.

I have not yet seen the russian garrison in Warzaw survive this and taking Warzaw this early seems to upset the Russian AI a little bit. The Russians will still come of course and you will soon need reinforcements but this will give you a bit of initiative and a chance to strike at perhaps one or two more garrisons, maybe not kills but wounding them.

how long does it take to repair cities? or is there an option?

Cities are slow to repair. I agree completely with striking to take out Warsaw as well. It is a must do move for the Germans. This slows the Russian army down getting into position.

I thought I was clever, too, making sure that extra garrison was there to deliver the knockout blow. And then once it didn't work... You never know!

I have used the same idea: capturing Warzaw as quickly as possible but I haven't been able to do it in only one turn yet.

It's not very smart to declare war before your troops are in good positions, which they usually aren't in CTGW.